Diplexers are used to combine satellite signals and CATV/UHF/VHF signals. You'll need a regular splitter for what you're trying to do, not a diplexer.
"Whenever I plug TV1 or TV2 thru the DC pass side of the diplexer, it doesn't work. Only the UHF/VHF side works."
That's the way it's supossed to be. The SAT side will pass thru 950 to 2300 MHz, the CATV/UHF/VHF side will pass thru 5 to 880 MHz. TV1 and TV2 signals are in the 5 to 880 MHz range.